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LC parallel circuit at resonant frequency

baristaskin

Dear All,

I am trying to simulate a simple LC parallel circuit when it is drived by a voltage source.

I'm expecting the current of the voltage source V1 to get smaller as its frequency gets closer to the resonant frequency.

When I simulate this circuit at the resonant frequency, with spectre default values, I get:

I tried to play around with the following parameters:

maxstep, reltol, vabstol, iabstol

without success.

My question is: how do I setup Spectre in order to get consistent and accurate results?

What I expect to see is a sine-shaped current signal with no DC value.

I'm including the netlist of the simulation shown above:

// Generated for: spectre
// Generated on: Mar 2 16:11:27 2015
// Design library name: paper3
// Design cell name: LC_osc
// Design view name: schematic
simulator lang=spectre
global 0
parameters _EXPR_8=1.986858915135295e-08 C=1p L=100n vdd=1 \
freqC=503.30696M cycles=10 L_IC=-sqrt(C/L)*vdd/2

// Library name: paper3
// Cell name: LC_osc
// View name: schematic
L1 (Vin 0) inductor l=L r=1a ic=0
V1 (Vin 0) vsource type=sine freq=freqC ampl=vdd/2 sinephase=90 sinedc=0
C1 (Vin 0) capacitor c=C ic=vdd/2
simulatorOptions options reltol=1e-3 vabstol=1e-6 iabstol=1e-12 temp=27 \
tnom=27 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 \
digits=5 cols=80 pivrel=1e-3 sensfile="../psf/sens.output" \
checklimitdest=psf
tran tran stop=_EXPR_8 errpreset=conservative write="spectre.ic" \
writefinal="spectre.fc" annotate=status maxiters=5
finalTimeOP info what=oppoint where=rawfile
modelParameter info what=models where=rawfile
element info what=inst where=rawfile
outputParameter info what=output where=rawfile
designParamVals info what=parameters where=rawfile
primitives info what=primitives where=rawfile
subckts info what=subckts where=rawfile
save Vin V1:p L1:1
saveOptions options save=allpub

 

Thank you in advance.

Parents

  • Dear baristaskin,

    This circuit will push the numerical accuracy of the simulation due to its infinite Q. As a result, you can try to force a very small time step to try to better estimate the period of the waveform. However, I would recommend lowering the Q a bit with a small resistor or pursuing a different simulation methodology.

    For example, if you are just trying to show that the LC impedance becomes very large as the frequency approaches resonance (and hence draws little current), perhaps you might run a small signal AC simulation of just the tank circuit and examine its input impedance. This can be done by applying an input current source across your network with AC magnitude  1 and sweeping the frequency across the resonant frequency of the tank. As the frequency approaches the resonance frequency, the magnitude of the impedance will become infinite - which indicates the current required ti sustain the tank is approaching 0. The result will appear as in Figure 1.

    I hope this helps!

    Shawn

    Figure 1

Reply

  • Dear baristaskin,

    This circuit will push the numerical accuracy of the simulation due to its infinite Q. As a result, you can try to force a very small time step to try to better estimate the period of the waveform. However, I would recommend lowering the Q a bit with a small resistor or pursuing a different simulation methodology.

    For example, if you are just trying to show that the LC impedance becomes very large as the frequency approaches resonance (and hence draws little current), perhaps you might run a small signal AC simulation of just the tank circuit and examine its input impedance. This can be done by applying an input current source across your network with AC magnitude  1 and sweeping the frequency across the resonant frequency of the tank. As the frequency approaches the resonance frequency, the magnitude of the impedance will become infinite - which indicates the current required ti sustain the tank is approaching 0. The result will appear as in Figure 1.

    I hope this helps!

    Shawn

    Figure 1

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